It is known to illuminate and view the end face of a length of foodstuff such as meat, using a video camera to obtain a video signal representation of visibly different regions in the end face, such a lean and fat regions, and to process the signal and compute for example the lean to fat ratio as well as the overall area of the end face.
The latter can be employed together with a density value for the foodstuff to compute the distance through which the foodstuff should be moved to enable a slice of a given weight to be cut from the length.
The lean to fat ratio can be compared with stored ratio values, to determine the quality of the portion, and this information can be used to direct the cut portion to one location or another, according to the lean/fat ratio which is usually a measure of the quality of the meat.
Difficulties have been experienced in accurately determining what in the camera field of view is product and what is supporting structure, so that the computation of the area is not always as accurate as it should be. Indeed a key difficulty in using vision systems to analyse product at the slicer cutting point is the acquisition of an accurate image and therefore video signal of the cut face of the product, clearly differentiated from the background to allow accurate image processing of the video signal and quantitative assessment of eg. fat to lean areas. This background may include parts of the machine itself, areas of product contamination and debris, and surface of the product which is not part of the cut face.
This has been approached previously by offsetting light sources to the side or below the product, to place non-product cut face material in shadow, in an attempt to allow video signals relating to it to be excluded from video signals relating to the cut face, by thresholding the signal from the camera. A problem with this approach is that conveyors and elements of machine structure close to the product face cast shadows across the face of the product, limiting the possible locations for the vision system components and restricting the possibilities for machine arrangement for optimal product handling
Other techniques have illuminated the sides of the product, casting the cut face in shadow, but this does not allow analysis of the cut face (eg to quantify lean to fat proportions of the cut face) which is now in shadow.
This allows the overall area of the cut face to be computed.
It has also been proposed to use light of different wavelengths, one for generating a structured light pattern of parallel lines across the face of the product and the other producing a monochromatic image of the product face and its surroundings. By processing signals derived from imaging the lines of the structured light, an electronic mask is produced corresponding to the product end face, which is used to gate signals relating to the monochromatic image to leave only the monochromatic image signals of the product face. The response time of such a system is limited by colour camera sensitivity, resolution and read-out time, and it cannot be used with some of the higher speed product slicing machines.
The present invention seeks to provide a vision system which has a higher speed of response than the previously proposed system which nevertheless can be used to produce accurate measurements of the end face of a length of foodstuff, especially meat, and in particular an accurate measurement of the area of the end face and of the ratio of one constituent part of the foodstuff from at least one other constituent part thereof, when both are present in the end face.
The invention also seeks to provide a video signal from which the shape of the end face can be determined by reference to pre-stored shape data.
Furthermore, the invention seeks to provide apparatus and methods by which data obtained by the improved vision system can be used to control the slicing and packaging of the sliced product.